1. Field of the Invention
The present invention refers to a grinding assembly for glass slabs and to a grinding head for a rectilinear grinding machine equipped with such system.
2. Background Art
As known, following etching and shearing operations, half-finished glass slabs are obtained, whose perimeter edges are in many cases ground in a grinding plant till the desired final geometry is reached. The grinding plants being used comprise a conveyor adapted to advance the glass slabs along an horizontal path through one or more working stations, each one of which houses a plurality of grinding wheels arranged in fixed positions along the path itself in order to grind two mutually opposite sides of the perimeter edge when advancing each slab.
The products obtained through the above-described known grinding plants have a not always satisfactory quality index, since, when the glass slabs advance along their related path, positioning and squaring errors of the slabs with respect to the grinding wheels can occur, so that the ground edges outlines sometimes are not perfectly straight or not perfectly orthogonal, with a scarce geometric accuracy of the finished product.
In order to simply and inexpensively solve the above mentioned problem, the Applicant of the present Application has filed patent EP-A-1468784, related to a grinding head 1 (see right side of FIG. 1) that allows accurately working each glass slab 2 in a working station where the slab 2 itself is kept in a univocal fixed reference position when working its related edge. A plurality of grinding heads 1, like the one disclosed in the above patent, are adapted to simultaneously work on all sides the glass slabs 2, through workings that are mutually different and are also operating at different speeds. The described grinding head 1, as shown in FIG. 1, substantially comprises, arranged in a row along the working direction of a glass slab 2: a grinding wheel 20 for the side grinding of the slab 2; a grinding wheel 22 for grinding the upper threads (or bevels) of the slab 2; a grinding wheel 24 for polishing the upper threads (or bevels) of the slab 2; a grinding wheel 26 for grinding the lower threads (or bevels) of the slab 2; a grinding wheel 28 for polishing the lower threads (or bevels) of the slab 2; and two grinding wheels 30, 32 for the side polishing of the slab 2. All grinding wheels 20 to 32 are supported and rotatingly driven by a respective spindle (not shown), and the grinding wheels 20 to 32 and their respective spindles are contained in and supported by a supporting structure 9.
It is also known that the removal capacity of a diamond grinding wheel in general essentially depends on its diameter. Therefore, when the head 1 must work very thick glass slabs 2, the grinding wheel 20 alone is not adequate for performing such working: it would therefore be necessary to provide for a grinding wheel 20 with a bigger diameter or an additional grinding wheel: both these solutions force to increase the width encumbrance of the head 1, and this is technically difficult, if not impossible, to carry out, since the heads 1 that can usually be found on a complete machine are at least four, in a mutual movement one with respect to the other along the sides of the glass slab 2 to be worked. In the end, the only possible solution with the current art technical knowledge is greatly increasing the grinding machine sides, which obviously is not preferable.